Iterative technique for the synthesis of optical-correlation filters

Optical-correlation filters that are translationally and rotationally invariant are made target specific by incorporating all the angular harmonics of the target image. An iterative design method similar to the technique of convex projections allows the image angular harmonics to be rephased so that the filter exhibits a constant-amplitude rotational response. Rotating this filter in the Fourier plane forms the Fourier summation of all angular harmonics of the input image. An image to be detected must have angular- harmonic terms that have an amplitude and a phase that are keyed exactly to the target image. This lock-and-tumbler filter exhibits excellent discrimination capability while preserving rotational invariance.